188 THe Bitack WATER OF DEE. 
6. The great width of the Cooran Gap caused by the stream 
working in a lateral direction argued another barrier to 
the south-east. This barrier (the Screel granite), with 
its wider plain structure, also implies lateral erosion, 
necessitating another barrier further south. 
7. If the river were continued in its natural course to the 
south-east the barrier would be found in the hard 
volcanic rocks of the Lake District. 
§. Of all the rivers crossing the Southern Uplands, only the 
Cooran-Screel was beheaded at this early stage. It 
follows that the piracy could only have been effected by 
a neighbouring river. 
The 650 Foot Plain. 
Eventually another uplift set in, which elevated the pre- 
vious base level at least 4oo feet. Immediately the river 
system of Galloway was rejuvenated. The streams ceased 
meandering on plains, and began anew to erode deep V 
notches into the old plain. This continued all the time of the 
uplift. When equilibrium was restored a new plain was pro- 
duced agreeing with the 650 feet contour line above present 
sea level. 
The peneplain character of this lower platform is more 
conspicuous and of greater area than that of the few remnants 
of the older 1000 foot stage. Along the South-West of Scot- 
land and the North-West of England this second plain is 
continually asserting itself. 
The Galloway streams worked out these peneplains in 
great detail, but the Cooran-Dee-Screel has engraved a clearer 
record of geographical development during the Pliocene 
Period than that given by any rival stream. 
This ancient river has left us a marvellous record of 
physiographic changes. It has registered an extraordinary 
series of misfits, captures, and contradictions. This is due to 
the obstructions which it met on its path—three distinct series 
of obstructions in the form of bosses of granite. They formed 
greater handicaps than were imposed on any other Scottish 
stream. 
A reconstruction of this 650 foot plain gives us two 
